Positive Bias Temperature Instability (PBTI) and Hot Carrier Injection (HCI) characterizations on InGaAs-On Insulator (OI) back gate nMOSFETs are presented and the degradation mechanism is discussed. Devices with two ultra-thin body thickness (15 nm and 8 nm) but same buried oxide (BOX) (15 nm) are investigated from a reliability perspective. Independent of the body thickness, the PBTI stress shows stronger impact on device performance than the HCI stress. Although the thinner body transistor exhibits a lower “off” current, it subjects to more severe degradations under both PBTI and HCI stresses. Pulsed HCI experiments confirmed that the self-heating effect (SHE) compounds the reliability challenge in ultra-thin body InGaAs-OI nMOSFETs. Additionally, it is also found that the different evolutions of the threshold voltage and the saturation current of the UTB InGaAs-OI nMOSFETs may be due to the slow border traps in the oxide.